Measurement and spectral analysis of spontaneous ion conductance fluctuations in the squid axon membrane constitute a significant direct source of information for comparison with kinetic schemes of the microscopic processes associated with ion channel gating in the neural membrane. A comparison between kinetic parameters derived from analysis of spontaneous fluctuations and the same parameters derived from linear perturbation analysis in the same axon should determine whether linear or non linear fluctuation theory applies at the microscopic level. Advanced, rapid measurement sequences will facilitate this comparison. The dependence of spectra on the time evolution (stationarity) of fluctuations will be assessed by "stroboscopic" noise measurements. Noise induced in axon ion channels by specific ions that react with membrane sites to modulate ion flows provide additional information on the basic conduction processes. Na conduction will be studied under new conditions that (1) eliminate the negative conductance property thereby producing stable measurements and (2) enable characterization of the Na activation kinetic process without inactivation. These measurements will be made in the stroboscopic mode, which will allow acquisition of data over a wide membrane potential range and provide better determination of the number of conducting states that ion channels have. In addition to ion channel gating noise, studies of the noise produced by the movement of ions through channels (transport noise) will be conducted under conditions that enhance the intensity of this source of noise.